Revert "Libeinfo: do not suppress ewarn() messages"

This reverts commit 4ee62c7903c65557c493f51d6703264a816156cd.

The previously referenced commit broke consistency because ewarnx() was
respecting the EINFO_QUIET environment setting, but after this commit,
ewarn() was not.
Also, due to discussion on the below referenced bugs, I think we do
want to suppress warnings when EINFO_QUIET=yes.

X-Gentoo-Bug: 482396
X-Gentoo-Bug: 439174
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=482396
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=439174